Shaft encoders are used as transducers for rotary movements, in the manufacture of printing presses primarily for the rotary movements of the printing cylinders. Prior-art shaft encoders convert a rotary movement according to the principle of the photoelectric scanning of DIADUR cyclotomies into electric signals, which are processed in numeric and memory-programmable controls or regulating devices or are used alone for position indication. Besides the incremental signals, a reference mark signal is additionally available for the reproduction of reference points. Prior-art shaft encoders have a rotor, which is rigidly connected to the shaft, whose angular position is to be determined, and a stator, which is rigidly connected to the press part in relation to which the corresponding angular position of the shaft is to be determined.
The problem occurs especially in the case of printing cylinders that can be pivoted off that besides the spin of a cylinder, i.e., rotation of the cylinder around its longitudinal axis, a pivoting movement around a pivot axis of the cylinder also takes place. The pivoting movement is superimposed to the spin of the cylinder. If a cylinder pivoted off is pivoted again onto its countercylinder into the printing position, the angular positions of the two printing cylinders must be exactly coordinated with one another, i.e., the rotary movements of the two cylinders must be synchronized during the pivoting up. This synchronization is especially problematic in the case of the flying change from one printing position to another, in which printing cylinders are pivoted in relation to one another and are brought into the printing position during full production. The two cylinders must run continuously synchronously during the pivoting up.
The zero position, i.e., the angular position which the cylinder pivoted off assumes in the printing position, changes continuously during the pivoting off and pivoting up in the case of prior-art shaft encoders. Due to the only finite velocity of the electronic control unit, this results in synchronization problems, as a consequence of which an appreciable loss of paper occurs until the two cylinders to be brought into the printing position are running perfectly synchronously.